Department of Radiation Oncology, University of Colorado School of Medicine, Aurora, CO 80045, USA.
Med Phys. 2012 Jun;39(6):3080-8. doi: 10.1118/1.4711813.
During stereotactic body radiation therapy (SBRT) for the treatment of prostate cancer, an inflatable endorectal balloon (ERB) may be used to reduce motion of the target and reduce the dose to the posterior rectal wall. This work assessed the dosimetric impact of manual interventions on ERB position in patients receiving prostate SBRT and investigated the impact of ERB interventions on prostate shape.
The data of seven consecutive patients receiving SBRT for the treatment of clinical stage T1cN0M0 prostate cancer enrolled in a multi-institutional, IRB-approved trial were analyzed. The SBRT dose was 50 Gy in five fractions to a planning target volume (PTV) that included the prostate (implanted with three fiducial markers) with a 3-5 mm margin. All plans were based on simulation images that included an ERB inflated with 60 cm(3) of air. Daily kilovoltage cone-beam computed tomography (CBCT) imaging was performed to localize the PTV, and an automated fusion with the planning images yielded displacements required for PTV relocalization. When the ERB volume and/or position were judged to yield inaccurate repositioning, manual adjustment (ERB reinflation and/or repositioning) was performed. Based on all 59 CBCT image sets acquired, a deformable registration algorithm was used to determine the dose received by, displacement of, and deformation of the prostate, bladder (BLA), and anterior rectal wall (ARW). This dose tracking methodology was applied to images taken before and after manual adjustment of the ERB (intervention), and the delivered dose was compared to that which would have been delivered in the absence of intervention.
Interventions occurred in 24 out of 35 (69%) of the treated fractions. The direct effect of these interventions was an increase in the prostate radiation dose that included 95% of the PTV (D95) from 9.6 ± 1.0 to 10.0 ± 0.2 Gy (p = 0.06) and an increase in prostate coverage from 94.0% ± 8.5% to 97.8% ± 1.9% (p = 0.03). Additionally, ERB interventions reduced prostate deformation in the anterior-posterior (AP) direction, reduced errors in the sagittal rotation of the prostate, and increased the similarity in shape of the prostate to the radiotherapy plan (increased Dice coefficient from 0.76 ± 0.06 to 0.80 ± 0.04, p = 0.01). Postintervention decreases in prostate volume receiving less than the prescribed dose and decreases in the voxel-wise displacement of the prostate, bladder, and anterior rectal wall were observed, which resulted in improved dose-volume histogram (DVH) characteristics.
Image-guided interventions in ERB volume and/or position during prostate SBRT were necessary to ensure the delivery of the dose distribution as planned. ERB interventions resulted in reductions in prostate deformations that would have prevented accurate localization of patient anatomy.
在立体定向体部放射治疗（SBRT）治疗前列腺癌期间，可使用可充气的直肠内气囊（ERB）来减少目标运动并降低后直肠壁的剂量。本研究评估了在接受前列腺 SBRT 治疗的患者中手动干预 ERB 位置对剂量的影响，并研究了 ERB 干预对前列腺形状的影响。
对在一项多机构、IRB 批准的试验中连续入组的 7 例接受 SBRT 治疗临床 T1cN0M0 期前列腺癌的患者数据进行了分析。SBRT 剂量为 50 Gy，分 5 次给予计划靶区（PTV），PTV 包括前列腺（植入 3 个基准标记物），边缘 3-5mm。所有计划均基于包括充气至 60cm³的 ERB 的模拟图像。每天进行千伏锥形束 CT（CBCT）成像以定位 PTV，并对计划图像进行自动融合，得出 PTV 重新定位所需的位移。当 ERB 体积和/或位置被判断为无法准确重新定位时，进行手动调整（ERB 再充气和/或重新定位）。基于获得的所有 59 个 CBCT 图像集，使用可变形配准算法确定前列腺、膀胱（BLA）和前直肠壁（ARW）的接受剂量、位移和变形。该剂量跟踪方法应用于 ERB 手动调整前后（干预）的图像，并比较干预前后的剂量。
35 个治疗部分中有 24 个（69%）进行了干预。这些干预的直接影响是增加了前列腺的放射剂量，包括 95%的 PTV（D95）从 9.6±1.0 增加到 10.0±0.2 Gy（p=0.06），前列腺覆盖率从 94.0%±8.5%增加到 97.8%±1.9%（p=0.03）。此外，ERB 干预减少了前列腺在前后（AP）方向的变形，减少了前列腺矢状旋转的误差，并增加了前列腺形状与放射治疗计划的相似性（Dice 系数从 0.76±0.06 增加到 0.80±0.04，p=0.01）。观察到前列腺体积减少接受低于规定剂量和前列腺、膀胱和前直肠壁的体素位移减少，这导致改善了剂量体积直方图（DVH）特征。
在前列腺 SBRT 期间对 ERB 体积和/或位置进行图像引导干预是确保按计划给予剂量分布所必需的。ERB 干预减少了前列腺变形，从而防止了患者解剖结构的准确定位。
